The present invention relates generally to a bank note validator and more specifically to a bank note or document validator designed to distinguish between authentic notes and documents and counterfeit notes and documents.
Bank note validators have answered the call of the marketers, by providing the ability to facilitate high cost transactions mechanically. Bank note validators are most popular in the beverage vending, food vending, product vending, gaming and wagering businesses. Change machines, i.e. currency to coin facilitating beverage, phone, and many other transactions are popular. In addition, bank note or currency validators are also used to authenticate such other financial instruments as stocks, bonds, and security documents. Therefore, as used herein, the term "bank notes" or "notes" will encompass all such applications.
Validation techniques have been consistently foiled by the ability of individuals to replicate the features inherent to bank notes with engineered facsimiles. The casual counterfeiter has at his disposal a variety of tools which are sufficient in generating reasonable facsimiles to foil even the best currency validator. Black and white copy machines, color copy machines, fax machines, ink jet copiers, computers and scanners are all tools which may be used to foil the common bank note validator. Some of these methods are very detailed and complex, yet none utilize the exact chemistry found in engraving dyes and inks used in bank note printing.
By far the greatest advancement in the bank note validator has been with the implementation of optical systems. The optical devices have been used transmissively and reflectively. Optical systems are very good at analyzing currency since all bills are designed to be recognized on sight by humans. Many features such as watermarks, security threads, and colored threads inserted as counterfeit deterrents are detectable primarily by sight. Therefore, it is reasonable to understand why people have high expectations towards electronic vision systems. Unfortunately, the human model for counterfeit detection cannot be built electronically into bank note validation systems because the cost would be prohibitive. A common method employed is to measure the signal responses reflected or transmitted through the printed and non-printed areas on the surface of a bank note, utilizing common light sources and comparing the result with an image stored in the currency validator memory. Major difficulties are encountered with properly detecting the very new bank note and the degraded image resulting from the worn bank note, compounded by printing misregistrations, while rejecting the acceptance of counterfeits.
Systems incorporating spectral analysis can overcome the difficulty of rejecting valid bank notes, even if very new or worn. In the performance of spectral analysis, it is possible to characterize the reflective, transmissive and absorptive properties inherent in genuine bank notes with light of wavelengths narrowly focused between ultraviolet and infrared. It is possible to determine the chemical composition of bank notes, as is employed in scientific analysis of other chemical studies, and store the results in a database for comparison later. In fact, utilizing the strictly controlled "chemical signature" of bank notes would be just the thing for detecting frauds and counterfeits. However, to implement such a spectrum analyzer in the bank note validation system would be prohibitive in both terms of expense and time required to perform a scan of the full light spectrum for each point along the length of a bank note.
Current spectral analysis technology typically uses one or more optical sensors to detect the optical reflection and/or absorption characteristics of bank notes. Many systems incorporate emitters and detectors operating in two or more wavelengths. These units usually take several points in discrete paths or channels along the long axis of a bank note. By comparing the sampled results with pre-stored results from real bank notes a determination can be made as to the type and genuineness of the bank note. Thus, the spectral analysis approach is not necessarily a fine resolution type system relying on the printed image of the bank note. It is a system which relies on the "signature bands" of genuine bank notes as they are generated by the absorbance, reflectance and transmission of specific wavelengths of light.
Typically the emitter/detector pairs comprise at least one set of infrared sensitive units. This allows data to be taken for almost all currencies, regardless of the visible color of the bank note. However, a drawback to this method is that a two-tone copy (black and white) or a copy made on colored paper can be devised that will produce data that mimics a real bank note, causing a counterfeit bank note to be accepted as genuine. As color copy technology has improved, it has also become possible to produce color copies almost identical in the visual spectrum with real bank notes.
Many countries constantly change their currency to limit counterfeit bank notes, cut production costs, improve longevity, etc. Several countries use different width bank notes as well. These different widths are difficult to accommodate in a single validation unit since the data channel for the narrower bank notes will vary depending on the insertion location in the unit. This usually requires several databases to be developed for one denomination. During the validation process it is necessary to scan each of these databases in succession and then decide if a match is possible. This can result in a process that takes several seconds, annoying or worrying the user.
Since most currencies in the world use different color combinations on different denominations, a validator that can detect these colors would be able to select which database to use to compare with the bank note. This would reduce the processing time significantly since only one set of databases needs searching. Two-tone copies might be eliminated since there would be no color in the data collected. Copies printed on color paper could also be eliminated since the subtle color variations on real currency would be missing. By comparing the color data with infrared data, acceptance of color copies may be greatly reduced.
Typical systems to detect color utilize three sensors for the Red, Green and Blue portions of the visible spectrum and a white light to illuminate the object. White light sources that produce an even spectrum of light are usually expensive, bulky or require an exotic power supply. In addition, they require frequent replacement and generate a large amount of heat, thereby affecting electrical circuitry. Each sensor has a filter to allow only a specific portion of the spectrum to pass. By combining the information from the three sensors and applying mathematical equations to the data, the color of an object can be determined.
In addition, due to variations in environment and the condition of the components, separate detectors and circuitry are required for the purpose of forming a reference point for relativity of subsequent measurements.
What all of the present bank note validators lack and what is desirable to have is the ability to quickly and accurately determine the authenticity of bank notes while keeping the cost and size of the validator to a minimum. Also lacking is the provision for compensation for variations in the environment or condition of the components using the circuiting already provided for validation determination. This long-standing but heretofore unfulfilled need for a compact and relatively inexpensive bank note validator that can quickly and accurately distinguish among authentic and counterfeit bank notes through spectral analysis is now fulfilled by the invention disclosed hereinafter.